Pneumatic tire having first and second turnup pads

ABSTRACT

A pneumatic tire construction is described suitable for severe loading conditions. The tire includes a bead portion further having an apex which extends radially outward of the bead core, and a first turn-up pad located adjacent said chafer, and a second turn-up pad located adjacent said first turn-up pad, wherein the first turn-up pad has a G′ less than the G′ of the second turn-up pad. Alternatively, the first turn-up pad may be located adjacent to the rim flange and the second turn-up pad may be located axially inward of the first pad. The second turn-up pad is preferably thicker and longer than the first turn-up pad.

TECHNICAL FIELD

This invention relates to heavy duty pneumatic tires such as arecommonly used on earthmoving equipment, aircraft, and agriculturaltires.

BACKGROUND

The invention concerns the reduction of rim chafing in large, heavy loadtires or Off-The-Road tires of radial construction that are used inheavily loaded vehicles. The lower sidewall of a typical radial OTRconstruction consists of a ply around the bead and chipperreinforcements that restrict the circumferential deformation of the ply.Under heavy load, the lower sidewall of the tire bends over the rimflange, and the ply reinforcement rotates in the circumferentialdirection. The severe deformation results in high ply cord compressionin the turnup near the rim flange region, and high in-plane shearstrains in the turn-up pad. The deformation also results in rubbing ofthe chafer against the rim flange, resulting in wear of both the tireand rim. Chafing can be minimized by using reinforcements in the lowersidewall, but this reduction is not very significant. Thus it is desiredto have an improved tire design to reduce the chafing of the tireagainst the rim.

DISCLOSURE OF THE INVENTION Definitions

“Aspect ratio” of the tire means the ratio of its section height (SH) toits section width (SW);

“Axial” and “axially” mean lines or directions that are parallel to theaxis of rotation of the tire;

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim;

“Belt reinforcing structure” means at least two layers of plies ofparallel cords, woven or unwoven, underlying the tread, unanchored tothe bead, and having both left and right cord angles in the range from17 degrees to 27 degrees with respect to the equatorial plane of thetire;

“Bias Ply Tire” means that the reinforcing cords in the carcass plyextend diagonally across the tire from bead-to-bead at about a 25-50°angle with respect to the equatorial plane of the tire, the ply cordsrunning at opposite angles in alternate layers;

“Carcass” means the tire structure apart from the belt structure, tread,under tread, and sidewall rubber over the plies, but including thebeads;

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection;

“Chafers” refers to narrow strips of material placed around the outsideof the bead to protect cord plies from the rim, distribute flexing abovethe rim, and to seal the tire;

“Chippers” means a reinforcement structure located in the bead portionof the tire;

“Cord” means one of the reinforcement strands of which the plies in thetire are comprised;

“Design rim” means a rim having a specified configuration and width. Forthe purposes of this specification, the design rim and design rim widthare as specified by the industry standards in effect in the location inwhich the tire is made. For example, in the United States, the designrims are as specified by the Tire and Rim Association. In Europe, therims are as specified in the European Tyre and Rim TechnicalOrganization—Standards Manual and the term design rim means the same asthe standard measurement rims. In Japan, the standard organization isThe Japan Automobile Tire Manufacturer's Association.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread;

“Innerliner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire;

“Normal rim diameter” means the average diameter of the rim flange atthe location where the bead portion of the tire seats;

“Normal inflation pressure” refers to the specific design inflationpressure and load assigned by the appropriate standards organization forthe service condition for the tire;

“Normal load” refers to the specific design inflation pressure and loadassigned by the appropriate standards organization for the servicecondition for the tire;

“Ply” means a continuous layer of rubber-coated parallel cords;

“Radial” and “radially” mean directions radially toward or away from theaxis of rotation of the tire;

“Radial-ply tire” means belted or circumferentially-restricted pneumatictire in which the ply cords which extend from the bead to bead are laidat cord angles between 65 degrees and 90 degrees with respect to theequatorial plane of the tire;

“Section height” (SH) means the radial distance from the nominal rimdiameter to the outer diameter of the tire at its equatorial plane; and,

“Section width” (SW) means the maximum linear distance parallel to theaxis of the tire and between the exterior of its sidewalls when andafter it has been inflated at normal pressure for 24 hours, butunloaded, excluding elevations of the sidewalls due to labeling,decoration or protective bands.

“Turn-up pad” means a strip of elastomer located between the chafer andthe turn-up end of the ply in the lower sidewall of the tire near thebead general area.

SUMMARY OF THE INVENTION

The invention provides in a first aspect a pneumatic tire having acarcass, the carcass having one or more cord reinforced plies and a pairof bead portions. Each bead portion has at least one annularinextensible bead core about which the cord reinforced plies arewrapped. A tread and a belt reinforcing structure is disposed radiallyoutward of the carcass. The bead portion further includes an apex whichextends radially outward of the bead core, and a chafer. The tirefurther has a first turn-up pad located adjacent said chafer, and asecond turn-up pad located between the plies and the first turn-up pad,wherein the first turn-up pad has a G′ less than the G′ of the secondturn-up pad.

BRIEF DESCRIPTION OF DRAWINGS

The invention may take physical form and certain parts and arrangementsof parts, several preferred embodiments of which will be described indetail in this specification and illustrated in the accompanyingdrawings which form a part whereof and wherein:

FIG. 1 is a cross-sectional view illustrating one side or one-half of asymmetrical heavy duty tire according to a first embodiment of theinvention;

FIG. 2 is an enlarged cross-sectional view of the bead portion of thetire shown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view illustrating the bead portionof a baseline tire;

FIG. 4 is an enlarged cross-sectional view of a second embodiment of abead portion of the tire of FIG. 1;

FIG. 5 illustrates a plot of Frictional Energy for the baseline tire andthe tire having the split pad design;

FIG. 6 is an enlarged cross-sectional view of a third embodiment of alower sidewall portion of a tire;

FIG. 7 illustrates an enlarged cross-sectional view of a lower sidewallportion of a tire illustrating how the turnup ply-turndown ply gauge,the turn-up pad gauge and the bead width are measured;

FIG. 8 illustrates a graph of ply cord compression for the tire of Ex. 1versus the base line tire;

FIG. 9 illustrates a graph of rim chafing indicator for the tire of Ex.1 versus the base line tire; and

FIG. 10 illustrates a graph of turn-up pad strain for the tire of Ex. 1versus the base line tire.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 and 2, a cross-sectional view of one half of atire of the present invention 10 is illustrated. The tire 10 has acarcass 14 which includes a crown region having a radially outer tread12 disposed over the crown region of the carcass 14. The outer surfaceof the tread may further include a plurality of lands and grooves or aplurality of tread blocks and grooves, as commonly known to thoseskilled in the art. The carcass further includes an optional inner liner17 that covers the entire interior facing surface of the tire carcassand serves to hold the air or gas mixture that is used to inflate thetire. The inner liner of the tire is typically made of butyl rubber. Thecarcass 14 further includes a pair of tire sidewalls 18 which extendradially inward from the outer radial surface of the of the tirecarcass, terminating in the vicinity of a pair of inextensible annulartensile members or beads 16.

The annular beads 16 illustrate an asymmetrical cross sectional shapehaving a lower half with a rounded outer surface 15 and an upper halfportion 33 with angular outer edges similar to half of a hexagon. Theannular beads may comprise other shapes such as, for example, round,hexagonal or a combination of shapes. Preferably, the radially innermostsurface 15 of the bead wire is rounded.

The carcass further includes one or more steel cord reinforced plies 19wrapped about each bead 16 forming a turnup portion 20, more preferablyan envelope turnup. The portion of the ply which extends from the crowntowards the bead and is axially inwards of the bead is referred to asthe down portion of the ply or down ply, while the portion of the plywhich extends radially and axially outwards from the bead is referred toas the up ply or turnup portion. The one or more plies 19 are orientedin the radial direction. Disposed radially outwardly of the ply 19 inthe crown area of the tire is a steel reinforced belt package 21 formedof two or more belts. A pair of sidewalls 18 extend radially inward fromthe tread 12 to the bead area. Located radially outward of the bead 16is an elastomeric apex 24. The apex as shown may have a triangularcross-sectional shape. Wrapped around the bead 16 is a flipper 26. Theflipper 26 is located adjacent the bead 16 and the carcass ply 19.Located on the axially outer edge of the bead area is a chafer 28.

A first turn-up pad 30 is located adjacent the chafer 28 in the beadportion of the tire. The first turn-up pad 30 has a first end 32 locatedin the vicinity of the bead wire 16, and more preferably in line withthe radially outer surface 33 of the bead wire. The first turn-up pad 30has a second end 34 located between the first end 32 and the ply turnup20. The length of the first turn-up pad 30 is sized so that it ispositioned over the 90 degree bend of the rim when the tire is underload. The first turn-up pad 30 has a thickness in the range of about 0.4to about 1.6 inches, and more preferably in the range of about 0.8 toabout 1.2 inches. The thickness of the turn-up pad 30 is measured acrossthe cross section of the pad, perpendicular to the pad longitudinalaxis. The length of the first turn-up pad 30 may range from about 200 mmto about 400 mm. The first turn-up pad 30 is comprised of an elastomericor rubber material having a G′ which ranges from about 0.25 MPA to about0.6 MPA, and more particularly in the range of about 0.35 MPA to about0.5 MPA, and more particularly about 0.35 to about 0.47 MPA. The firstturn-up pad 30 is made of a material having a G″ which ranges from about0.05 MPA to about 0.8 MPA, and more particularly about 0.05 MPA to about0.07 MPA.

Unless otherwise noted, all G′ values are measured on a rubber sample ata sample temperature of 90 deg C, at a measurement frequency of 10 Hzand at a strain amplitude of 50%. The rubber sample is taken from acured tire manufactured to the desired manufacturer specifications. Forthe purposes of this invention, the storage modulus property G′ is aviscoelastic property of a rubber composition and may be determined by adynamic mechanical analyzer over a range of frequencies, temperature andstrain amplitude. One example of a dynamic mechanical analyzer (DMA)suitable for measuring G′, G″ is model number DMA+450 sold by the 01-dBMetravib company. The DMA instrument uses dynamic mechanical analysis toevaluate rubber compositions. A cured sample of the respective rubbercomposition is subjected to a precisely controlled dynamic excitation(frequency and amplitude) at a frequency (Hertz) and temperature (° C.)and the sample stress response is observed by the instrument. Theobserved sample response can be separated, by the instrument, intoviscous or loss modulus (G″) and elastic or storage modulus (G′)components. Unless otherwise indicated, all G″ are measured at the sameconditions as G′.

A second turn-up pad 40 is located adjacent said first turn-up pad 30,and is preferably located between the first turn-up pad 30 and the ply19. The second turn-up pad 40 has a thickness in the range of about 0.4to about 2.0 inches, and more preferably in the range of about 0.8 toabout 1.8 inch. The length of the second turn-up pad 40 may range fromabout 200 mm to about 500 mm. The second turn-up pad 40 is comprised ofan elastomeric or rubber material having a storage modulus G′ whichranges from about 0.05 MPA to about 2.0 MPA and more preferably in therange of 0.6 to 1.5 MPA and more preferably in the range of 0.8 to 1.2MPA. The turn-up pad 30 is made of a material having a G″ which rangesfrom about 0.05 MPA to about 0.1 MPA. Thus it is desired that the firstturn-up pad 30 be about 40% to about 60% softer than the second turn-uppad 40. Thus it is desired that the first turn-up pad 30 have a G′ about40% to about 60% less than the G′ of the second turn-up pad 40, morepreferably about 45% to about 55% less, and most preferably about 50%less.

As shown in FIG. 2, the length and thickness of the first turn-up pad 30is about the same or slightly smaller than the second turn-up pad 40. Areduction in the stiffness of rubber of the first turn-up pad 30minimizes the tangential traction between the chafer 28 and rim therebysignificantly reducing rim chafing. Finite element analysis of theinvention has shown significant reduction in rim chafing. FIG. 5illustrates the calculated accumulated frictional energy levels of thebaseline turn-up pad of FIG. 3 versus the accumulated frictional energylevel of the split pad of FIG. 2. The baseline turn-up pad has a G′similar to that of second turn-up pad 40 and a thickness of 0.79 inchesat a radius of 4 inches from the bead center, and a thickness of 1.76inches at a radius of 8 inches from the bead center. With the split padembodiment, rim chafing between chafer and rim is reduced by 18-22%.

FIG. 4 illustrates a second embodiment of the invention wherein thefirst turn-up pad 50 has a modified geometry. The first turn-up pad 50is located in the region where the sidewall contacts the rim flange at aradius R, wherein R ranges from 5 to about 8 inches and has a minimumthickness in the range of about 0.8 to 1.2 inches. The first end 52 ofthe first turn-up pad 50 is located radially outward of the bead, andhas a second end 54 that is located radially inward of the outer tip ofthe apex. The first turn-up pad 50 is comprised of an elastomeric orrubber material having a G′ which ranges from about 0.25 MPA to about0.6 MPA, and more particularly in the range of about 0.35 MPA to about0.47 MPA, and more particularly about 0.4 to about 0.45 MPA. The firstturn-up pad 30 is made of a material having a G″ which ranges from about0.05 MPA to about 0.08 MPA.

As shown in FIG. 4, the second turn-up pad 60 has a maximum thickness ofabout 1.5 to 2 times as thick as the first turn-up pad 50. The secondturn-up pad 60 has a first end 62 located about at the annular bead, anda second end 64 which extends radially outward of the apex tip and thesecond end 54 of the first turn-up pad 50. The length of the secondturn-up pad is about 1.5 to 3 times the length of the first turn-up pad.The second turn-up pad 60 is comprised of an elastomeric or rubbermaterial having a storage modulus G′ which ranges from about 0.5 MPA toabout 2.0 MPA and more preferably in the range of 0.6 to 1.5 MPA andmore preferably in the range of 0.8 to 1.2 MPA. The turn-up pad 30 ismade of a material having a G″ which ranges from about 0.05 MPA to about0.1 MPA.

FIG. 6 illustrates yet another alternate embodiment of a tire 100 of thepresent invention illustrating only the bead and lower sidewall area.The remaining areas of the tire are as described in more detail, above.When there is a durability issue in the lower sidewall, tire designershave historically increased the bead diameter in order to reduce thestress/strain in the lower sidewall. An increase in bead width increasesthe compressive force in the ply cord while achieving only moderatedecrease in the stress/strain in the lower sidewall. The inventor hasfound that a combination of reduction in bead width and increase inturn-up pad thickness yields the most desirable results that are notintuitive. It is desirable to reduce the bead width Bw of the annulartensile member 16 to the range of about 2.0 to 3 inches, moreparticularly in the range of about 2.4 to 2.65 inches, and morepreferably about 2.4 to 2.5 inches.

It has also been determined that by reducing the gauge or distancebetween the ply turnup and the ply turndown (hereinafter“turnup-turndown gauge”) as shown in FIG. 7, that the ply cordcompression is reduced. The inventor has found that the effect ofdecreasing the gauge between ply turnup and ply turndown on the ply cordcompression is more pronounced as the turn-up pad gauge increases. Thedistance or gauge is measured perpendicular to the longitudinal axis ofthe ply. It is thus desired to have the turnup-turndown gauge to be inthe range of about 0.25 in to about 0.8 in, and more particularly in therange of about 0.4 inch to about 0.6 inches, and most preferably about0.4 to about 0.5 inches. The turnup-turndown gauge is measured over arange of radius R from the center of annular tensile member to theintersection with the turnup longitudinal axis. It is additionallypreferred that the turnup-turndown gauge previously stated occur at aradius of 8 inches from the bead center. At a radius of 4 inches fromthe bead center, it is desired to have the turnup-turndown gauge to bein the range of about 1.25 in to about 1.75 in, and more particularly inthe range of about 1.4 inch to about 1.7 inches, and most preferablyabout 1.5 to about 1.6 inches.

FIG. 6 further illustrates a first turn-up pad 110 and a second turn-uppad 120. The first turn-up pad 110 has a minimum thickness T1 in therange of about 0.5 inches to about 1.7 inches, and more preferably inthe range of about 0.6 inches to about 1.2 inches. The thickness ismeasured at a defined radius from the bead center, and is determinedperpendicular to the longitudinal axis of the ply reinforcement. Theminimum thickness of the first turn-up pad is determined over a range ofradius R as measured from the center of the annular tensile member. TheRadius R ranges from about 4 to about 8 inches. The length of the firstturn-up pad 110 may range from about 200 mm to about 400 mm. The firstturn-up pad 110 has a maximum thickness in the range of about 1.3 inchesto about 3 inches, and more preferably in the range of about 1.3 inchesto about 2 inches, preferably at a Radius R of 8 inches.

The second turn-up pad 120 is located between the first turn-up pad andthe ply turnup, and is preferably located between the first turn-up pad110 and the ply 19. The second turn-up pad 120 has a minimum thicknessin the range of about 0.5 inches to about 1.7 inches, and morepreferably in the range of about 0.5 inches to about 1.2 inches. Thesecond turn-up pad 120 has a maximum thickness in the range of about 1.3inches to about 3 inches, and more preferably in the range of about 1.3inches to about 2 inches. The thickness of the second turn-up pad isdetermined at a first radius R measured from the center of the annulartensile member. The maximum thickness preferably occurs over the rangein radius R of about 6 to 8 inches from the bead center, and the minimumthickness preferably occurs over the range in radius R of about 4-6inches. The length of the second turn-up pad 120 may range from about200 mm to about 500 mm.

The first turn-up pad 110 is comprised of an elastomeric or rubbermaterial having a G′ which ranges from about 0.25 MPA to about 0.6 MPA,and more particularly in the range of about 0.35 MPA to about 0.47 MPA,and more particularly about 0.4 to about 0.45 MPA. The first turn-up pad110 is made of a material having a G″ which ranges from about 0.05 MPAto about 0.08 MPA.

The second turn-up pad 120 is comprised of an elastomeric or rubbermaterial having a storage modulus G′ which ranges from about 0.5 MPA toabout 2.0 MPA and more preferably in the range of 0.6 to 1.5 MPA andmore preferably in the range of 0.8 to 1.2 MPA. The turn-up pad 120 ismade of a material having a G″ which ranges from about 0.05 MPA to about0.1 MPA.

FIGS. 8 through 10 illustrate the results from numerical simulationstudy of a tire of the invention in a 57 inch size and a 63 inch size ascompared to a baseline design in a 57 inch and 63 inch size. Thebaseline design had a bead width of 3.15 inch and a turnup-turndowngauge of 1.13 inches at a radius of 8 inches from the bead center. Thebaseline tire had a turn-up pad gauge of 1.75 inches as measured at aradius of 8 inches from the bead center. The Ex. 1 tire had an annulartensile member having a width of 2.65 inch, and a turn-up pad thicknessof 2.52 inches. The pad was evenly divided into two materials as shownin FIG. 6, wherein the G′ of the axially outer turn-up pad 110 was 0.4to 1.2 MPA and the G′ of the axially inner turn-up pad was 0.8 to 2.8MPA. The thickness of each turn-up pad was 0.5 inches to about 1.3inches at a radius of 4 inches to 8 inches from the bead center. The Ex.1 tire had a bead width of 2.65 inches, a ply turnup ply-turndown gaugeof 0.45 inches at a radius of 8 inches from the bead center.

FIG. 8 illustrates a significant 55% reduction of ply cord compressionfor the inventive tire of Ex. 1 as compared to the baseline design. FIG.9 illustrates a reduction of 16% in the rim chafing indicator for thetire of Ex. 1 as compared to the baseline tire. FIG. 10 illustrates thatthe strain in the turn-up pad is about the same for the base line designand the tire of Ex. 1.

What is claimed is:
 1. A pneumatic tire comprising a carcass, thecarcass having one or more cord reinforced plies and a pair of beadportions, each bead portion having at least one annular inextensiblebead core about which the cord reinforced plies are wrapped, a tread, apair of sidewalls, each sidewall extending radially inward from thetread to one of the pair of bead portions, and a belt reinforcingstructure disposed radially outward of the carcass, each bead portionfurther comprising an apex which extends radially outward of the atleast one bead core, and a chafer, said one or more cord reinforcedcarcass plies having a turndown portion which extends from the crown andaxially inward of the at least one bead core in each bead portion and aturn up portion in each bead portion which extends radially outward fromthe at least one bead core and axially outward of the at least one beadcore, the tire further comprising in each bead portion a first turn-uppad located adjacent said chafer, and a second turn-up pad locatedbetween the turnups of the one or more cord reinforced carcass plies andsaid first turn-up pad, wherein the first turn-up pad has a G′ less thanthe G′ of the second turn-up pad, wherein at a radius of 4 inchesmeasured from the center of the bead core to the intersection with theturnup longitudinal axis, the longitudinal axes of said turnup andturndown portions are parallel, and wherein the gauge between the turnupportion of the ply and the turndown portion of the ply measuredperpendicular to the longitudinal axes is in the range of 1.25 inch to1.75 inches.
 2. The tire of claim 1 wherein the G′ of the first turn-uppad is in the range of 20% to 60% less than the G′ of the second turn-uppad.
 3. The tire of claim 1 wherein the G′ of the first turn-up pad isin the range of 30% to 55% less than the G′ of the second turn-up pad.4. The tire of claim 1 wherein the G′ of the first turn-up pad is in therange of 40% to 55% less than the G′ of the second turn-up pad.
 5. Thetire of claim 1 wherein the first turn-up pad has a radially outer endwhich is radially outward of said apex.
 6. The tire of claim 1 whereinthe second turn-up pad has a radially outer end which is radiallyoutward of said apex.
 7. The tire of claim 1 wherein the first turn-uppad has a radially outer end which is radially inward of a radiallyouter tip of said apex.
 8. The tire of claim 1 wherein the bead core hasa width less than 3.2 inches.
 9. The tire of claim 1 wherein the beadcore has a width in the range of 2.4 to 2.5 inches.
 10. The tire ofclaim 1 wherein the bead core has a width in the range of 2.4 to 2.65inches.
 11. The tire of claim 1 wherein the bead core has a width in therange of 2 to 3 inches.